This invention relates to spacers for aerial cables for supporting one or more electrical conductor cables above the ground.
Overhead conductor cables are commonly suspended from a messenger cable usually made of steel. The messenger cable is supported on poles or towers with the conductor cable spacers arranged at spaced intervals along the messenger cable to suspend one or more conductor cables. Since many power circuits require three phase electric power, it is often convenient to suspend conductor cables in groups of three employing a spacer which supports all three conductor cables and simultaneously maintains the conductors in spaced relation.
If the advantages of suspending conductors in this manner are to be fully availed, it is essential that the spacer be easily attached to the messenger cable and to the conductor cables.
To provide ease of attaching the spacer to the messenger and conductor cables and to reduce the number of parts required, the means for retaining the cables in their respective seats of the body member of the spacer should accommodate messenger and conductor cables of varying cross sectional diameters without providing bushings, sleeves, grommets or the like of different sizes to surround the cables at their seats.
The construction of the spacer should be such that all of its parts have both high mechanical strength and high electrical strength and are durable in use.
In addition, all parts of the spacer should be economical to manufacture and to assemble to the final form of the spacer.
There has been a long felt need for spacers for aerial cables to solve the above-mentioned objectives.
On June 23, 1959 U.S. Pat. No. 2,891,751 was granted to Essex Wire Corporation. The spacer disclosed in that patent comprised three major elements, a body member, a clamping member and a cam lever. The clamping member was pivotally secured to the body member by a metal rivet and the cam lever was pivotally secured to the body member by a headed stud. A generally concave seat or channel received a bushing or sleeve through which the messenger cable passed. Three generally concave seats or channels received three bushings or sleeves through which three conductor cables passed respectively. The clamping member was provided with three outwardly projecting arms and, upon rotation of the clamping member in one direction, the ends of these arms closed the open faces of the seats and engaged the peripheries of the bushings or sleeves surrounding the conductor cables located in the seats.
Upon rotation of the clamping member in the same direction, its cam surface engaged the cam arm or the cam lever causing the cam lever to be rotated about a pivot to close the open face of the messenger seat and to engage the periphery of the bushing or sleeve surrounding the messenger cable in that seat.
The clamping member was locked in closed position by a coil spring and metal latch pin, the end of which was urged into a hole in the body member. To unlock the latch it was necessary to insert the end of a rod, nail or similar instrument into the hole and press the latch against the coil spring until the end of the latch passed completely out of the hole.
To the best of our knowledge, the spacer of this patent has never met with any commercial acceptance in this country, doubtless for reasons which include the following:
1. it contained metal parts thereby adversely affecting the electrical strength of the spacer;
2. bushings or sleeves of different sizes were required to accommodate messenger and conductor cables of different diameters;
3. the parts could not all be molded at the same time from a single mold because they were made of different materials; and
4. it was expensive to manufacture, assemble and install because eleven parts were required, namely two pivot pins, three main spacer parts, two locking member parts, and four bushings or sleeves.
On Mar. 21, 1961 U.S. Pat. No. 2,976,344 was granted to Robert L. Bethel. The spacer disclosed in this patent consisted of four links the ends of which were secured together by hinges or knuckles and cup screws having flanges and polygonal heads. The heads were tightened or loosened by a socket wrench. The messenger cable was surrounded by a grommet made of rubber or plastic. The conductor cables insulated by sheaths of polyethylene were surrounded by grommets also made of rubber or plastic.
To install the spacer on messenger and conductor cables, the parts of the lower cup screw were disengaged and the other cup screws were loosened. Then the upper ends of the upper two links were separated by rotating them about the loosened upper cup screw and then they were rotated towards each other until their semi-cylindrical recesses gripped the grommet of the messenger cable. Then the lower ends of the upper and lower links were rotated towards each other until their semicylindrical recesses engaged the grommets surrounding the insulation of the cables. Then the parts of the lower cup screw were engaged and all of the cup screws were tightened so that all of the grommets were gripped tightly by the semi-cylindrical recesses at the junctions of the links.
To the best of our knowledge, the spacer of this patent was never manufactured or sold commercially in this country, doubtless for reasons which include the following:
1. grommets of different sizes were required to accommodate messenger cables and conductor cables of different diameters;
2. it was very difficult to install because of the time consuming installation of the grommets about the cables and the time consuming successive rotations of the four links about the four cup screws and then the successive tightening of the cup screws; and
3. it was expensive to manufacture and to assemble because (1) the parts could not all be molded at the same time from a single mold and (2) at least nine parts were required, namely, at least one cup screw part, one threaded stud, the four links, a Nylon bushing, and grommets of at least two different sizes, one for the smaller diameter messenger cable and another for the conductor cables.
On Jan. 24, 1967 U.S. Pat. No. 3,300,576 was granted to Hendrix Wire & Cable Corp., the owner of the present patent application. The body of the spacer disclosed in said patent was made of high density polyethylene which has a low dielectric constant and is weather and track resistant.
The body was provided with a generally concave messenger seat and three generally concave conductor cable seats. Elastic ties were provided, each having a ring at each end and a plurality of ball-like enlargements adjacent to one or both ends. These ties were made of polyurethane which has a low dielectric constant and is weather and track resistant. However, because the body of the spacer and the ties were made from different plastic materials, one mold could not be used to mold both the body of the spacer and the ties at the same time from a mold cut to make both of them.
To apply the tie to a conductor cable located in a seat, it was necessary to insert a reduced portion near one end of the tie into one of the slots provided in the lower edge of the member forming one of the conductor cable seats, pass the tie around the insulation of the conductor cable, stretch the tie very tightly about the cable and insert a reduced portion near one of the enlargements into another slot.
In 1969 Hendrix Wire & Cable Corp. introduced to the market in this country what it called its "LLD-7PD" and "LLD-15PD" spacers. The body of each spacer was of an open diamond shape somewhat like that shown in the Bethel patent but it was molded in one piece of high density polyethylene. The body had generally concave seats, one to receive a messenger cable and three to receive conductor cables. Each of the ties for retaining the cables in the seats was a hollow oval shape having a ring at one end. They were called "RT Ring Ties". They were made of thermoplastic polyurethane, ethyl propylene rubber (vulcanized or cross linked) or thermoplastic rubber, all weather and track resistant materials which are stretchable. The ties and body of the spacer could not be molded at the same time from one mold because they were made of different thermoplastic materials.
Slots were provided in the lower edges of the members forming the conductor cable seats similar to the slots in U.S. Pat. No. 3,300,576. Slots were also provided in the upper edge of the member forming the concave messenger cable seat. The ring ties were applied to a cable by inserting one end of the loop of the tie in one of the slots, grasping the ring at the other end, stretching the tie over an insulated conductor cable and then inserting the loop at the end of the tie adjacent to the ring in another slot adjacent to the first slot.
It was necessary to provide ring ties of five different lengths to accommodate conductor cables and messenger cables of different diameters.
These ties were an improvement upon the ties shown in U.S. Pat. No. 3,300,576 but they were expensive to manufacture and difficult and time consuming to apply to a cable because of the necessity of exerting very strong stretching forces upon them while they were being applied.
The spacer for aerial cables of the present invention is a great improvement upon all of the aforesaid prior art and it satisfies the long-felt need for spacers which solve the abovementioned objectives.